When electronic devices, such as IC devices, are mounted, it is necessary to form conducting wirings through a semiconductor supporting substrate. As a method of forming conductor wirings in such supporting substrate, it is performed to form many through holes in the supporting substrate and to form a metal electrode on a side wall face of the through hole. As to a diameter of the through hole, it is demanded reduction of a size of the hole to 100 μm or smaller, for example, and it is further demanded to form many holes at a high density. Further, as a material of the supporting substrate, a high resistance is required for suppressing leak current between the wirings.
Further, as it is demanded to make such substrate thinner for attending the need of reducing the heights of electronic devices, a high strength is required for the material of the substrate, On the other hand, since the substrate is divided into individual pieces by dicing after mounting electronic devices thereon, properties such as ease of cutting is also demanded.
It is known to form through holes in a high resistance silicon substrate. In this case, photolithography and DRIE are combined to form the through holes.
In the case that higher dielectric strength voltage is required for an insulating substrate, a sapphire substrate is used. In this case, laser processing technique is generally used. In this case, however, due to the influences during the laser processing or deterioration of a substrate strength in the case of forming many holes, the sapphire substrate itself may be broken. Particularly, it is considered that the yield is lowered as the density of the through holes becomes higher.
According to patent documents 1 and 2, it is described that through hole electrodes are formed in a wafer made of a ceramics such as alumina. It is further described that through holes are formed in the wafer by laser processing.
According to patent documents 3, through holes are formed in a ceramic substrate and the through holes are formed in a green sheet for the ceramic substrate by pins. According to patent document 4, it is also described that the through electrodes are formed in the ceramic substrate.
Further, according to patent document 5, laser is irradiated to a green sheet of a ceramic substrate such as alumina to form through holes each having a diameter of 100 μm or smaller.